Techniques are conventionally known in liquid-crystal illumination systems which apply a light integrator so as to reduce illumination unevenness. Also, due to the recent strong demand for higher resolution displays, many liquid-crystal panels now have more picture elements to satisfy this demand, which has also resulted in projection lenses often requiring more lens elements in order to reduce aberrations to an acceptable level while projecting images formed on liquid crystal panels having higher resolution displays. As a result of these trends toward higher resolution, there has been an accompanying tendency for vignetting of liquid-crystal panels to increase and the transmission factor of projection lenses to decrease, thereby lowering the illumination at a viewing screen.
Therefore, in order to maintain a bright display image in higher resolution displays, there is greater need to accurately match the location of an illuminating light beam to the location of the liquid-crystal panel, thereby obtaining a maximum illumination at the viewing screen.
However, any attempt to more accurately match the location of an illuminating light beam with that of a liquid-crystal panel in order to generate a brighter display generates a need to adjust for deviations in the positioning of the illuminating light beam as a result of production tolerances and errors that occur, for example, in the positioning of the filament of a light source to its base and in the positioning and alignment of other optical components used to produce the light beam which illuminates the liquid crystal panel.
One known method of adjusting for such deviations between a liquid-crystal panel and an illuminating light beam includes shifting, in a plane normal to the optical axis, the position of a lens which transmits polychromatic light from a light source before separating the polychromatic light into three colors. However, in this method, the amount of shifting of the lens relative to the adjustment of the illuminating light beam is roughly one to one, and thus the amount of shifting required so as to adjust the location of the illumination becomes large, which thereby enlarges the size of the illumination system as a whole. Further, a mechanism with sufficient driving power to shift the lens a large amount is also required, resulting in higher cost.
Another method for maintaining sufficient brightness at the viewing screen is to increase the intensity of the illuminating light source. However, this requires that additional measures be taken to deal with the additional heat generated from a higher intensity light source and, therefore, this approach is considered impractical.
In the illumination optics of an endoscope, it is known to shift a light source together with a reflector, or to shift a converging lens, so as to prevent a decline in illumination caused by deviations of an illuminating light beam. However, the illumination optics of a liquid-crystal projector are larger, as a whole, than the illumination optics of an endoscope. Thus, it is considered impractical to adopt such techniques for use with a liquid-crystal projector.